Glutamate in enteral nutrition: can glutamate replace glutamine in supplementation to enteral nutrition in burned rats?

Background: Glutamine (GLN) plays many important roles for the enterocytes in health and disease, but no liquid enteral products contain GLN because of its instability. We hypothesized that glutamate (GLU) may replace GLN in supplementation to an enteral diet, and compared the metabolic effect of GLU and GLN on the gut to each other. Methods: Rats suffering from a 30% burn received an enteral diet containing 30% GLU (m/w to total amino acids; GLU group), 30% GLN (GLN group), or a standard amino acid formula (CTR group). After a 64-hour feeding period, the small intestine and the portal and arterial blood were harvested to observe portal and arterial amino acid levels, and glutaminase activity and glutathione in the jejunal mucosa. In another study, 3 H uptake into the mucosal protein was examined after a massive dose injection of 3 H-phenylalanine. Results: Alanine, a product of GLN or GLU catabolism, significantly increased in the portal blood of the GLU group compared with the GLN group. In the gut mucosa of the GLU group, 3 H uptake into protein and total glutathione were higher than those of other two groups. GLN did not elevate the glutaminase activity. Arterial GLU levels increased in the GLU group, however remained within safety limits. Conclusions: Enterally delivered GLU may be a preferable fuel for the enterocytes and enhance the mucosal protein synthesis. GLU probably can substitute for GLN in supplementation to an enteral diet regarding many roles GLN plays in the intestinal mucosa under stress situations.